Oversteer "Snap Back"

[BOSSSTANG]

Hello everyone, I have a question that maybe some of you suspension guru's can answer. I have driven many cars to the limit of adhesion but I will say that my Mustang is the only car that "snaps back" while over steering, as in when the car is in a "stable" drift, it all of a sudden swings back the other way. Is this a common trait of the Mustang? Or do I have something set up bass ackwards on my suspension?


My suspension set up currently: H&R race springs, koni yellows, standard front sway bar, Strano rear bar on medium, watts link, Bob's LCA's and Roush non adjustable UCA. I also run a square set up of 18x9.5 w/ 275/35/40 Michelin Pilot Sports.

 

[Grant 302]

How many of those other cars were RWD and live axle?

The issue sounds like driver error. The answer IMO is coordinating the inputs from your right foot and your hands. Sounds like lift throttle oversteer. So stay 'in it' more or unwind your counter steer faster as front grip increases.

 

[wwilde001]

I have had it happen to me several times. The car will break loose in the back, and by the book, the instructors tell you to let off the throttle and turn into the skid...right. In all cases as soon as it stopped one way it snaps back the other way (aka a tank slapper). So the last time this happened I anticipated the snap back and made the timely correction the other way. It finally settled out with only two off instead of four! So keep on correcting until is stops.

 

[DGRacing]

Couple thoughts on this. A good suspension (none of the oem stuff ) can absorb much of that kinetic energy properly (converting it internally to heat where it is dissipated).

Second. If the car is corner balanced it will reduce this effect since the fulcrum the car is trying to rotate on will be closer to true center as opposed to forward bias.

 

[cosm3os]

I have had it happen to me several times. The car will break loose in the back, and by the book, the instructors tell you to let off the throttle and turn into the skid...right. In all cases as soon as it stopped one way it snaps back the other way (aka a tank slapper). So the last time this happened I anticipated the snap back and made the timely correction the other way. It finally settled out with only two off instead of four! So keep on correcting until is stops.

If that's what a HPDE instructor told you, don't go back to that club!

You are describing oversteer. The cause: decreased grip in the rear and/or increased grip in the front. When the rear starts coming around, you need to figure out if it is because you have applied an inappropriate amount of throttle (throttle oversteer) or you have too much grip in the front (either from set up, or the application of brakes or lift of throttle mid corner). My guess is its not set up. My guess, give that we are talking about 444 hp/ 290 hp cars is you have applied an injudicious amount of throttle. You are spinning the rears, and when you lift, you are stopping them from spinning and thus giving them back grip. But that's not the end of the story here.

Assuming that's the case, what do you do? Well, the "book" you quoted is the exact wrong thing. As soon as you lift, you may be stopping the rears spinning under power, but you have transferred the weight of the car onto the fronts--so you have ended up right where you started: understeer. Yes, you turn the wheel in the direction of the skid (to avoid continuing all the way around), but to end the event altogether, you have to correct the oversteer. You are in a tank slapper because you caught the first slide by turning the wheel, but you haven't solved the rear grip problem, so the rear is now ready to "follow" the front tires in the direction they are turned. So it starts skidding back the other way!

The solution is to "keep your foot in it". That's easy in a low power car that doesn't break traction under throttle like a Miata or an E30 BMW--you just keep applying power so the weight transfers back instead of forward and eventually the rear will get the grip (countersteering all the way, of course).

In our cars, this takes a lot of feel and experience. You can't lift too much or too abruptly cause you transfer weight forward. You can't keep the throttle where you have it cause you are spinning the rears. You have to find the balance point and, ultimately, stay ahead of the car by anticipating the car's inclination to rotate the other way. Its all about being smooth enough to reduce the severity of the transitions back and forth.

My .02 without being in the right seat.

 

[BOSSSTANG]

Have never driven a live rear axle car before, all have been IRS.

Here is the situation in question, come to think of it, you can see HLT say "SHIFT NOW" so maybe I did lift (or ran out of RPM). Either way, glad it ended ok with the only a broken tire valve stem and paying a $425 bill for 17 fire extinguishers. I also had this same thing happen to me a friend when he was doing burn outs in parking lot, that is why I wanted to ask here to see if anyone has had this same feeling before. I know how to drift pretty well in most other cars, but this mustang does not inspire confidence like the other cars did, maybe it is the extra HP/speed.

https://www.youtube.com/watch?v=iJ9zpkCnKPg

 

[DGRacing]

Assuming that's the case, what do you do? Well, the "book" you quoted is the exact wrong thing. As soon as you lift, you may be stopping the rears spinning under power, but you have transferred the weight of the car onto the fronts--so you have ended up right where you started: understeer. Yes, you turn the wheel in the direction of the skid (to avoid continuing all the way around), but to end the event altogether, you have to correct the oversteer. You are in a tank slapper because you caught the first slide by turning the wheel, but you haven't solved the rear grip problem, so the rear is now ready to "follow" the front tires in the direction they are turned. So it starts skidding back the other way!

The solution is to "keep your foot in it". That's easy in a low power car that doesn't break traction under throttle like a Miata or an E30 BMW--you just keep applying power so the weight transfers back instead of forward and eventually the rear will get the grip (countersteering all the way, of course).

In our cars, this takes a lot of feel and experience. You can't lift too much or too abruptly cause you transfer weight forward. You can't keep the throttle where you have it cause you are spinning the rears.

Good write up.

There's a third option and the better choice than lifting or doing nothing and that's short shifting. Take the higher gear quickly. This will reduce the wheel torque allowing the tires to re-engage the surface without either slowing them too much or unloading them from weight transfer.

 

[fuhrius]

If that's what a HPDE instructor told you, don't go back to that club!

You are describing oversteer. The cause: decreased grip in the rear and/or increased grip in the front. When the rear starts coming around, you need to figure out if it is because you have applied an inappropriate amount of throttle (throttle oversteer) or you have too much grip in the front (either from set up, or the application of brakes or lift of throttle mid corner). My guess is its not set up. My guess, give that we are talking about 444 hp/ 290 hp cars is you have applied an injudicious amount of throttle. You are spinning the rears, and when you lift, you are stopping them from spinning and thus giving them back grip. But that's not the end of the story here.

Assuming that's the case, what do you do? Well, the "book" you quoted is the exact wrong thing. As soon as you lift, you may be stopping the rears spinning under power, but you have transferred the weight of the car onto the fronts--so you have ended up right where you started: understeer. Yes, you turn the wheel in the direction of the skid (to avoid continuing all the way around), but to end the event altogether, you have to correct the oversteer. You are in a tank slapper because you caught the first slide by turning the wheel, but you haven't solved the rear grip problem, so the rear is now ready to "follow" the front tires in the direction they are turned. So it starts skidding back the other way!

The solution is to "keep your foot in it". That's easy in a low power car that doesn't break traction under throttle like a Miata or an E30 BMW--you just keep applying power so the weight transfers back instead of forward and eventually the rear will get the grip (countersteering all the way, of course).

In our cars, this takes a lot of feel and experience. You can't lift too much or too abruptly cause you transfer weight forward. You can't keep the throttle where you have it cause you are spinning the rears. You have to find the balance point and, ultimately, stay ahead of the car by anticipating the car's inclination to rotate the other way. Its all about being smooth enough to reduce the severity of the transitions back and forth.

My .02 without being in the right seat.

This. on many points. Smooth being the key...always easier to monday morning QB but you looked like you were fighting that car hard about three corners before your problem corner (the whole video you posted)...but your signature indicates you're a fairly experienced driver...so that was confusing to me when I saw the video. A key difference in the mustang is the less-than-subtle weight transfer rear-to-front with the stock suspension...but I also see that you've modded the suspension so who knows. it's also a function of the live axle when you're talking about weight transfer when you're cornering as opposed to purely in a straight line. I think it's trickier under lateral load than an IRS car.
On corner entry it felt like you got a lot of weight to the front (maybe even got some corner-entry understeer but hard to tell without being in the car), then got the rear to start rotating, but it sounds like there wasn't much lift of the accelerator at all (too much, as has been pointed out, can lead to trouble...but not enough can too)...then your countersteer set you up for going left as soon as the front got grip. I wonder if there was a traction-control intervention in there somewhere or if there's a camber/rise in that corner that we can't see on that video that would have given you a quick bit of additional bite in the front...and as soon as the fronts hooked up pointed left...the car's likely to follow.
It's interesting that if you take accelerator / brake inputs out of the discussion for a minute and just think about weight transfer and steering input, what you just did was essentially a pendulum turn (or, in rally speak, a scandanavian flick) where you intentionally set up this dynamic that some people might call a tank-slapper or whatever.

(description from wikipedia: While approaching the turn, the driver applies a slight steering input to the opposite direction of the turn, then steering into the turn, while sharply lifting off the throttle and (in some cases, depending on speed and type of layout) lightly applying the brakes. This will cause the car to slide sideways facing slightly away from the turn. Then steering input is applied towards the turn and as the driver releases the brake pedal while still holding down the throttle the car will slingshot itself around the corner to the desired direction. Of course, countersteering will again be required to control the induced oversteer.)

The more you've swung the ass out in the first few steps, the more quickly / violently it'll come back...though it's usually not 'violent' in a rally car since there's such little lateral grip.
You just did it on a less-forgiving surface because when your sticky rubber regains traction and it's backed by a heavy right foot...well, the video shows the result.

 

[cosm3os]

Short shifting in the middle of that would have been worse. That'd give you even more dramatic weight transfer than lifting.

From the vid, it looks pretty clear that you were in throttle oversteer, and alot of it compounded by even more throttle it sounds like. It required so much oppolock, I don't know if much could have saved it. You even seemed to be pretty quick with your hands.

Best to be smoother with the throttle on and avoid the situation! Nice to live another day!

 

[BOSSSTANG]

In our cars, this takes a lot of feel and experience. You can't lift too much or too abruptly cause you transfer weight forward. You can't keep the throttle where you have it cause you are spinning the rears. You have to find the balance point and, ultimately, stay ahead of the car by anticipating the car's inclination to rotate the other way. Its all about being smooth enough to reduce the severity of the transitions back and forth.

My .02 without being in the right seat.

I guess that makes some sense, I am used to driving mid engined or rear engined cars so there is a lot of weight in the back to keep the tires from spinning, where as in the Mustang all the weight is in the front and there is more torque to break the rear wheels loose. Your point about me giving it more gas once the rear was already loose makes sense now, I did not think of it like that before, I'm used to just pouring in the gas and letting all that weight in the rear do its job and propel me forward, even thought the Atom has a hp to weight ratio of ~7 lb per RWHP and the mustang is ~10 lb per RWHP I think the weight distribution has a big thing to do with it (ie car layout). Maybe I just need to go play on the skid pad and figure this thing out then because I guess like you said I haven't had a car with that much power (or that light in the rear) to have to let up on the gas! I would (and I guess we all would!) like to think that I have good car control from my previous experience, but this Mustang has humbled me and left me confused and questioning my ability!

In all, I am glad it did not end up worse, like lifting as soon as I started drifting and kissing that inside wall, or even worse t-boning the pit in wall. phew!

 

[VoodooBoss]

Keep in mind that all of you are way more experienced than me but as someone else noticed you seemed to be fighting the car a lot before you went off track. So with that in mind did you setup your Boss for square or was it that way when you purchased it? You're also running a narrow tire compared to many of us. If you're fighting your car that much all around the track you might check your sway bar settings and confer with others on your setup.

 

[DGRacing]

Short shifting in the middle of that would have been worse. That'd give you even more dramatic weight transfer than lifting.

No.
WHAT IS SHORT SHIFTING?: http://youtu.be/dSc0PkaPsXk

 

[Roadhouse]

I'm glad you got the car stopped when you did

I'm in the "driver error" camp. Lots of good info in here. I have done the same thing...

 

[Swede]

Re: Oversteer "Snap Back"

Looking at the slomo, I think it looks like you were countersteering a bit too much and when the rear tires regained traction, the front wheels were pointing too much to the left.. Hard to say just from a video, though.

What TC setting where you on?

Glad you didn't hit anything... You ended up quite close to the trees...

/Swede

 

[cosm3os]

No.
WHAT IS SHORT SHIFTING?: http://youtu.be/dSc0PkaPsXk

Agree with everything said in that video, but that's not the answer here (at least at the point that the OP was in trouble). The technique in the video was corner exit throttle oversteer. The OP's oversteer starts and turn in and gets worse mid corner. In other words, he's still turning whereas the Nissan is getting the car straight so the weight transfer to the front with the shift is a non issue.

 

[fuhrius]

Agree with everything said in that video, but that's not the answer here (at least at the point that the OP was in trouble). The technique in the video was corner exit throttle oversteer. The OP's oversteer starts and turn in and gets worse mid corner. In other words, he's still turning whereas the Nissan is getting the car straight so the weight transfer to the front with the shift is a non issue.

agreed...the nissan didn't have much oversteer at all (just look at the steering wheel input)...just had a lot of wheelspin. a short shift is definitely a good technique for reducing wheelspin but the more oversteer there is, the trickier it would be to manage the car.

 

[DGRacing]

Agree with everything said in that video, but that's not the answer here (at least at the point that the OP was in trouble). The technique in the video was corner exit throttle oversteer. The OP's oversteer starts and turn in and gets worse mid corner. In other words, he's still turning whereas the Nissan is getting the car straight so the weight transfer to the front with the shift is a non issue.

Fair point. I mainly replied with that technique when you were discussing general over steer conditions and the dilemma of lifting or not. I guess for this technique a throttle induced oversteer would be the more likely cause but its a fine line. Unless you are coasting, if the drive wheels start to overslip its often because of accelerating beyond their slip limit in the context of a turn (i.e. you're not just skating in neutral).

Assuming that's the case, what do you do? Well, the "book" you quoted is the exact wrong thing. As soon as you lift, you may be stopping the rears spinning under power,

and

The solution is to "keep your foot in it"

So I should have said that I wasn't necessarily addressing the OPs problem per se, it could have been a couple of things happening at once, but injecting another (3rd) possible way to address this condition (in general) the books don't often mention. In particular I've used this a couple times at VIR between 5 and 5a which is a broad arc you are accelerating through right into back to back turns, if the tires start to spin from throttle you can have a real problem if you don't correct it. Lifting makes it worse. And the "snap back" effect happens a lot right at that location. I've seen two mustangs literally destroy each other on a warm up lap because of it. Anyway, I just threw another technique in people sometimes overlook when its often the best solution. YMMV.

agreed...the nissan didn't have much oversteer at all (just look at the steering wheel input)...just had a lot of wheelspin. a short shift is definitely a good technique for reducing wheelspin but the more oversteer there is, the trickier it would be to manage the car.

Yep. There is a point beyond which short shifting to settle the rear is not the best solution. Even still, the goal is to get the rear wheels untorqued and re-engaged, in my opinion, regardless of what caused the original slippage. They need to have power to get the car moving in the direction of the nose and you don't want to power them in a high rpm gear, thus taking the upper gear without also unloading them is one approach.

 

[blacksheep-1]

If that's what a HPDE instructor told you, don't go back to that club!

I agree. although jumping out of the throttle seems like the correct thing to do, it actually is counter productive in that it unloads the rear tires even more. I haven't observed "snap oversteer" nearly as much in these cars as th eold FOX body cars, which was so prevalent you just expected it on every turn.

Have you considered running softer spring and shock setting in the rear or a smaller sway bar...or conversely, going the exact opposite in the front. IF this is not a driver initiated problem I would pull about 4 pounds out of the rear tires, and/or put about 4 pounds in the front to quickly check this theory. Tire pressures are sort of a crutch for handling but they can quickly point you in the right direction for chassis adjustments.

 

[further]

Finally checked out the video. Woah, you just missed that wall. Could have been pretty gnarley. Glad your ok.

So my understanding is that snap over steer occurs when throttle is lifted, mid turn. It should be a steady squeeze of increasing throttle through the double apex.

There is a ton of traction down there in Hogpen, but the bottom line is, you're running as fast on street tires that others run on slicks. Yeah, front sway bar on full stiff and rear bar off or 18 mm.

 

[blacksheep-1]

That's one of the reasons, the transition from turn it to turn out and managing that part of the car's suspension is pretty involved. FWIW have you been to a driver's school or had an instructor ride with you (and not the one you mentioned) maybe a skippy school would be in order?